(a) Technical Field
The present invention relates to a hydrogen generation apparatus. More particularly, the present invention relates to a hydrogen generation apparatus, which can generate a hydrogen gas by hydrolysis of a chemical hydride to use it as a fuel supply source for a fuel cell system using a hydrogen gas as a fuel.
(b) Background Art
A fuel cell is a generator which converts chemical energy of a fuel into electric energy by an electrochemical reaction within a fuel cell stack. The fuel cell can be used to supply power to small-sized electric/electronic devices or portable devices as well as power for industrial and home uses and for vehicle operation.
A fuel cell under extensive research is a fuel cell using hydrogen as a fuel while using oxygen as an oxidant to be used as a power source for vehicle operation, for example, a polymer electrolyte membrane fuel cell or a proton exchange membrane fuel cell (“PEMFC”).
Preferred examples of the hydrogen storage system available at present include high-pressure hydrogen, liquefied hydrogen, metal hydride, chemical hydride, carbon nano-tube, etc. Of these, in particular, methods using the high-pressure hydrogen and the liquefied hydrogen have been most developed. However, in the case of a hydrogen storage system using high-pressure hydrogen, weight storage density of the hydrogen is very low, thus necessitating a very large volume to achieve a target driving distance, which results in a problem in vehicle package. Here, the amount of the hydrogen storage may be increased by increasing the pressure but it may reduce safety and increase cost.
In the example of a hydrogen storage system that uses a liquefied hydrogen, the hydrogen storage density is higher than the high-pressure hydrogen, but a relatively low temperature (25K, 1 atm) must be always maintained, and further there is a boil-off problem.
As an alternative, a new hydrogen storage system using a metal hydride (“MH”) and a chemical hydride have been developed. [We would prefer not to characterize the background art].
A hydrogen storage system using a metal hydride is a system which can adjust temperature and pressure of the hydrogen storage metal to store and emit hydrogen. The hydrogen storage system using a metal hydride requires a temperature higher than 150° C. for a reversible reaction, so that inhale/exhale can be readily performed. However, hydrogen in the amount of less than that of the theoretical hydrogen storage is usually inhaled/exhaled within the reversible range of the hydrogen inhale/exhale, and the reaction is performed rather slowly.
The hydrogen storage system using a chemical hydride is a system which generates hydrogen through hydrolysis of a hydride containing hydrogen. In the system using a chemical hydride, the hydrogen storage amount becomes twice as much as that of the hydrogen storage capacity of a hydride because, in this system, an additional amount of hydrogen, which is equal to that of hydrogen contained in the hydride, is obtained by hydrolysis of water in addition to the hydrogen contained in the hydride itself. Moreover, when the hydrogen is generated by the reaction, the heat produced is not very high, and the pressure is almost at the level of atmospheric pressure and thus, the system can be managed rather safely. However, the chemical hydride is not easy to control for the reaction, and also the reaction is irreversible, thus requiring additional reproducing process.
Examples of conventional chemical hydrides include NaBH4 and LiBH4. These chemical hydrides are suitable for small scale hydrogen generation and are also considered safe. However, these materials are rather sensitive to humidity of air, unstable, and are considered as not easy to handle. Moreover, by-products produced during the reaction tend to deteriorate the progress of reactions of the remaining reactants.
Efforts have been made to introduce a catalyst in the system to accelerate the reaction. However, expensive precious metals such as Pt and Pt—Re/alumina have been excluded due to their high cost and thus most work has been performed using low-cost catalysts instead.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.